Piezoelectric crystal



Nov. 19, 1946. s, x SHQRE I 2,411,298

PIEZOELECTRIC CRYSTAL Filed Feb. 12, 1945 .STANDIIP SIDNEY X SHORE 'INVENTOR Biffi/wwf# aci agee crystal wafer for vibrating the same at a supersonic frequency thereby producing supersonic agitation of the etching solution. Electrical connections to the etching solutions are made by electrode plates iS--l6, for example, of copper. The crystal wafer i3 is completely immersed in the etching solution and to minimize direct electrical conduction between the compartments the barrier formed by the crystal wafer is preferably supplemented by means of an insulating masking element il of hard rubber which barrier extends beyond the surface of the etching solution.

In carrying out the process yin accordancewith the invention, a crystal .Wafer it is cut to the de.. sired shape and to a thickness greater than the thickness corresponding to the desired resonant frequency. 'lire rough cut wafer may then be machine lapped to a thickness value corresponding to or greater than the thickness at which heretofore the manual processing of wai-'ei' was initiated.,

For vibrating the crystal wafer at a supersonic frequency the wafer is coupled to an oscillator, for example, of the type shown in Fig. 2. The oscillator shown comprises a discharge tube 2@ having a cathode iii, a control grid 22 and an anode 2t connected in feedback relationship in known manner to an inductance-capacitance tuned circuit 2li-25 having a resonant frequency in the supersonic range, i. e.`, a resonant frequency greater than about 25 kilocycles. A selfregulating operating bias voltage for the tube 2K9 is provided by means of a grid-leak resistor 2t. Ammeter 2l serves as a grid-current indicator during operation of the oscillator. The crystal Wafer to be processed is connected across the resonant circuit 2l-25 by means of conductors aixed to the electrode plates ib-ld (see Fig. 1).

The 'cutting of the wafer from the mother crystal and the subsequent lapping thereof produces a substantial amount of disordered crystal line material in microscopic form which remains on the surface of the wafer and/or within the microscopic cavities produced by the crystalline elements protruding from the surface of the crystal, Bly immersing the wafer in an etching solution agitated at supersonic frequency the wafer is subjected simultaneously to chemical action and to the action of the kinetic energy forces iinparted to the solution by the supersonic agitationl and it is found that the disordered crystalline material is substantially completely removed as Well as those microscopic crystals which are only partially etched out by the chemical action and thus non-permanently secured to the crystal wafer.

In the preferred arrangement of my invention, the constants of the tuned circuit ffii-25 are so selected that the resonant frequency of the tuned circuit approximates the resonant frequency of the crystal Wafer whereby the crystal wafer vibrates at its resonant frequency and becomes the 1 frequency determining element of the oscillator.

frequency of the wafer compared with a signal voltage of the desired frequency derived from a frequency standard 3i. The beat frequency produced by detector St is applied to a frequency meter 3l and the etching of the wafer is terminated when the resonant frequency of the wafer f attains a predetermined value With respect to the Siti frequency of the standard 3i as indicated by the frequency meter 32.

While I have described my invention by means of specific examples and in specific embodiments I do not wish to be limited thereto for obvious modications will occur to those skilled in the art without departing from the spirit and scope Qf the invention.

What I claim l. En the manufacture of piezo-electric eiements the steps comprising immersing a crystal element in an etching solution and etching the surface of the element so immersed while similitaneously vibrating eiement and agite-.ting said solution at a supersonic frequency.

Z. in the manufacture of piezo-electric elements the steps comprising predimensioning a crystal element to a resonant frequency greater than about 25 kilocycles, immersing the predimensioned element in an etching solution, and etching the surface of said element so immersed while simultaneously'vibrating the element and agitating said solution at the resonant frequency of the element.,

3. The method of manufacturing a piezo-electric element having a predetermined resonant y frequency, comprising predimensioning a crystal Wafer to a resonant frequency greater than about 25 kilocycles, immersing the predimensioned element in an etching solution, etching the surface of said element so immersed while simultaneously vibrating the element and agitating said solution at the resonant frequencyiof the element, measuring the resonant frequency of the element, and terminating said etching when the, resonant frequency of the element equals the said predetermined resonant frequency.

d. Apparatus for processing piezoelectric elements, comprising a. vcontainer for an etching solution, means to so position the element in the container that the major surfaces of the element are exposed to the etching solution and the ele ment divides the container into two compart ments, and means to electrically connect the etching solution in each of said compartments to a source of electrical potential.

5.` Apparatus for processing piezo-electric elements, comprising a container for an etching solution, means to so position the element-in the container that the major surfaces of the element are exposed to the etching solution and the ele- Yment divides the container into two compartments, and means coupled to said element. through the etching solution to vibrate the velement at a super-sonic frequency.

6. Apparatus for processing piezo-electric elements, comprising a container for an etching solution, means to so position the element in the container that the major surfaces of the elementare exposed to the etching solution and the element divides the container into two compart' ments, means coupled to theelement through the .SENEY X, SHURE. 

